1. Field of the Invention
The present invention is broadly concerned with composites and methods of using those composites for sorbing and/or destroying dangerous substances such as chemical and biological warfare agents and environmental pollutants in air, water, hydrocarbon or fuel streams, and soil. The methods of the invention are carried out by simply contacting the target substance with metal oxide nanoparticles coated with carbon.
2. Description of the Prior Art
Nanocrystals of common metal oxides such as MgO, CaO, ZnO, TiO2, Al2O3, and Fe2O3, have been shown to be highly efficient and active adsorbents for many toxic chemicals including air pollutants, chemical warfare agents, and acid gases. In most cases, destructive adsorption takes place on the surface of the nanocrystals, so that the adsorbate is chemically dismantled and thereby made nontoxic. In particular, aerogel-prepared (AP) nanocrystalline MgO has been shown to have small average particle sizes (˜4 nm), high surface areas (>500 m2/g) and high reactivities. Klabunde et al., J. Phys. Chem., 1996, 100, 12142; S. Utamapanya et al., Chem. Mater., 1991, 3, 175, each incorporated by reference herein.
The use of these nanocrystalline metal oxides is limited under conditions where liquid water or water vapor is present due to the tendency of the oxides to adsorb water, and thereby be partially deactivated toward adsorption of the target pollutants. Although the target pollutants are usually subjected to conversion in the presence of water as well, relatively large amounts of water can mitigate against the adsorption of the target adsorbate, decreasing the efficiency of the destructive adsorbent.
Activated carbon is primarily made of graphitic structures which exhibit a less polar surface. Activated carbon has a lower tendency to adsorb water than nanocrystalline metal oxide surfaces do. Moreover, activated carbon is itself a widely used adsorbent against unwanted fluids or the like.